Screening Of Germplasm For Resistance To Late Blight

In this research, 210 clones, which were extensively selected from 7 crosses involving Neo-tuberosum in their background in seedling generation, were evaluated for foliar and tuber resistance to late blight by observing late blight resistance of field-planted potatoes in different locations and years, and inoculating detached leaves and tuber slices. The stability of resistance was analyzed, and some materials with good resistance to late blight were selected, which may be used as parents in breeding for late blight resistance, or as parents in additional cycle of recurrent selection. The data obtained can be used for setting up a database, which may be helpful for breeders to use them efficiently in a potato breeding program. Crosses were analyzed for their ability to produce a high percentage of clones with good resistance and agronomic characters, and heterosis in use of Neo-tuberosum in potato breeding was discussed. Also, the physiological races in Harbin and Keshan were isolated and identified, which may be useful information when plant materials were evaluated for their late blight resistance. The results are as following.1. Thirty samples, which were collected from Harbin and Keshan in different years, were separated and identified. Seven compound physiological races of phytophthora infestans were detected. They are 0.3.7, 0.3.4.7, 0.3.4.7.11, 0.3.4.7.8.11, 0.3.4.7.8, 0.3.4.7.9.11 and 0.3.4.7.8.9.11. The last one is more virulent than any other races.2. One hundred and sixty three clones with foliar resistance to late blight were selected out of 210 clones tested, accounting for 77.62%, of which 109 clones had good stability, 72 clones had high resistance to late blight, 153 clones gave yield more than 500 g per hill, and 103 clones had specific gravity more than 1.090. Considering overall characters, 98 clones were selected.3. Eighty three clones with tuber resistance were selected out of 210 clones tested, accounting for 39.25%, of which 20 clones expressed high resistance, 79 clones yielded over 500 g per hill, and 56 clones had specific gravity of over 1.0900. Fifty three clones were selected when overall characters were considered.4. Seventy clones were selected with both foliar and tuber resistance to late blight, of which 66 clones gave yield of more than 500 g per hill, 44 clones had specific gravity of more than 1.0900, and overall, 40 clones performed well.5. A database about late blight resistance was set up combining with other botanic characters.6. The percentage of resistant clones in crosses was investigated through inoculation of Phytothoratha infestans to detached leaves and tuber slices. As S. tuberosum increased its percentage in hybrid pedigree, the resistance decreased, indicating the importance of Neo-tuberosum in late blight resistance. By investigating the percentage of clones selected with acceptable plant characters and tuber resistance to late blight in crosses in seedling generation of 2002, it was indicated that the combination of Neo-tuberosum x S. tuberosum was better than any other combination, suggesting the expression of heterosis in the cross of Neo-tuberosum x S.tuberosum7. Nine clones with both foliar and tuber resistance, and acceptable agronomic characters as well were selected in this research, which may be directly used as parents for improvement of potato cultivars.